This invention relates broadly to the art of endless-conveyor-belt monitoring systems and more particularly to roller-type belt switches, and the like used to determine when belt conveyors are not moving or are moving too slowly.
Roller-type switches, and the like, are often used to monitor conveying systems for purposes of "sequencing" and determining belt slippage. In the case of sequencing, in coal mines for example, endless conveyors operate in interrelated systems in which tributary conveyors empty into main conveyors. If a main conveyor in such a system should stop due to a malfunction, for example, the tributary conveyor(s) feeding the stopped main conveyor must automatically stop. Roller switches are used to monitor the main conveyors in such systems.
With regard to slippage detection, endless conveyors, again in coal mines for example, sometimes become overloaded or unduly slippery. In these cases, the conveyor belts can begin to slip on their drive rollers and thereby cause undue heat, possibly burning the belts. Again, roller switches are used to determine when belts are not moving at a sufficient speed to thereby provide indications of slippage.
In many modern underground coal mines, conveyor belts 9 are mounted on wire ropes, or cables, 10 such as are depicted in FIGS. 1 and 2. In such cases, there is a conveying portion 12 of the belt and a return portion 14. The conveying portion 12 is carried on trough guide rollers 16, 18, and 20 which are arranged to shape the conveying portion 12 of the belt into a trough for holding coal 22. The return portion 14 of the belt 9 rides on straight guide rollers 24.
In the prior art, most roller switches have the appearance of the roller switch 26 depicted generally in FIGS. 1 and 3. This prior-art roller switch includes a heavy, full length, straight roller 28, end supports 30 at the opposite ends of the heavy roller 28, and a centrifugal switch 32 attached to the shaft of the heavy roller 28. The end supports 30 normally have bearings for supporting the heavy roller 28, the belt resting thereon, and the centrifugal switch 32.
In practice, the prior-art roller switch of FIGS. 1 and 3, to applicant's knowledge, is usually supported by ground supports 36 which are built up from the ground 34 to a proper height for causing the correct degree of loading by the belt return portion 14 on the roller 28. Although this arrangement is uncomplicated it has several difficulties. Firstly, the heavy roller 28 and belt return portion 14 cause an undue load on the bearings, thereby unduly reducing the lives of these bearings. Secondly, since the heavy roller 28 operates on the outside, or dirty side, of the belt return portion 14, an undue amount of water and coal dust "gob off" from the return portion 14 onto the heavy roller 28. This material causes slippage between the heavy roller 28 and the conveyor belt and also frequently jams operation of the heavy roller 28. In cold weather the problem is further complicated when the "gob off" material freezes.
Still another problem with the prior-art belt-switch system of FIGS. 1 and 3 is that the pressure of the heavy roller 28 pushing upwardly on the otherwise unloaded belt return portion 14 sometimes gets it out of alignment on the straight guide rollers 24.
It is therefore an object of this invention to provide a belt switch which not only is easy to install, but which also does not require undue loads on bearings, which operates on the clean sides of conveyor belts, and which does not tend to get conveyor belts out of alignment.
Several U.S. patents disclosing prior-art roller switches include U.S. Pat. No. 2,510,163 to Wood and 2,589,220 to Buckeridge. In both of these patents the rollers of roller switches are supported by bearings located at opposite ends of what appear to be full length, heavy, rollers. Although in both cases, the rollers operate on the clean undersides of belt conveying portions, the mounting systems for these roller switches are relatively complicated (they usually require rigid mounting structures from the ground and cannot easily be mounted on conveyor-supporting wire ropes 10, for example) and the same statements made above as to the wearing of bearings apply to the apparatus of these patents. Further, installation of roller switches between conveying and return belt portions does not eliminate the "gobbing off" problem since dust and chunks of the materials being conveyed fall from the conveying portion of the belt and collect on the relatively massive structure of the roller assembly.
Many prior-art roller-type belt switch systems employ centrifugal switches 32 as is mentioned above. Such a centrifugal switch is disclosed in U.S. Pat. No. 433,549 to Soule. However, at least one prior-art roller switch, that of Wood U.S. Pat. No. (2,510,163), utilizes a rotor being magnetically coupled to a pivotal member. When Wood's roller is driven, the rotor, apparently via magnetic flux, also rotates the pivotal member to close switch contacts. In both the centrifugal switches and in the magnetically operated switch of Wood, there are rigid contacts which physically come together. Such contacts have relatively short lives. Thus, it is an object of this invention to provide a detecting switch for a roller switch which is dependable in operation and has a relatively long life.
It is also an object of this invention to provide a detecting switch which is smooth in operation and has little wear due to friction or jerky operation.
Some newer, "solid state" belt switches do not have moving parts, but rather are coupled to monitored belts by means of magnetic and/or electrical fields. Although these systems are effective in some cases, they are often rather complicated and expensive to repair. Thus, it is another object of this invention to provide a belt switch which is relatively uncomplicated and inexpensive to repair.